vSAN performance diagnostics reports: "Too many IOs are handled by a vSCSI adapter"

Products

• VMware vSAN

Issue/Introduction

This article explains the vSAN performance diagnostics issue: "Too many IOs are handled by a vSCSI adapter", why it might be showing up, and what possible solutions there are to address the issue.

Symptoms:

In vSAN performance diagnostics, you see the error message:

Too many IOs are handled by a vSCSI adapter

Environment

VMware vSAN 6.6.x
VMware vSAN 6.7.x

Cause

This means that a single vSCSI adapter is probably a performance bottleneck because it is handling much more IOPS than desired. The following screenshot shows a vSCSI adapter handling much more read IOs per second compared to the desired threshold.

 

 

 

Performance may be improved by assigning the VM disks to multiple vSCSI adapters, so that the IOs can be load-balanced across the vSCSI adapters.

Resolution

VMware recommends that a PVSCSI adapter be used for the best performance. (To see how to use a PVSCSI adapter in your configuration, please refer to KB 1010398). Each VM can have a maximum of four adapters. To achieve the best IOPS and throughput performance, you must create four adapters for each VM. You must then distribute the VM disks across all four adapters.